In mounting a crank or lever on a working shaft, the arm is usually provided with an annular collar member at one end that embraces the end of the shaft. A highly effective way of mounting and locking the annular member to the shaft is to provide internal tapered involute splines on the annular member and mating external tapered involute splines on the end of the shaft.
A particular application of this mechanical connection technology, indeed the application where it was first used, is in the mounting of a pitman arm to the output shaft of a power steering gear. There is an important reason why this connection was invented in this environment. One standard mounting of the steering gear on large trucks positions the pitman arm outside the frame of the vehicle. The left front tire of the vehicle is normally in a position to come into close proximity to the frame and thus in direct conflict with the pitman arm and the end of the shaft when a hard right turn is made. The original invention obviated this interference problem by eliminating the draw down nut and lock washer at the end of the shaft.
This successful approach to solving this problem is found in the prior U.S. patent to Richard H. Sheppard, Joint Between Output Shaft and Pitman Arm, U.S. Pat. No. 3,338,603, issued Aug. 29, 1967. The patent specifically sets forth the concept of tapered involute splines for connecting the parts, and, more importantly, for the purpose of locking the two parts together so that under normal operating conditions the two parts are like one. In fact, tests have shown that during operation of a power steering gear with the splined connection of the '603 patent, the parts retain their original tightness. The oscillating motion of the arm actually causes the annular mounting member to tend to creep tighter and tighter on the end of the tapered shaft with each cycle of operation, thus automatically assuring that the parts do not separate.
In order to initially install the pitman arm with the designed tightness on the tapered, splined end of the output shaft, it has been common practice to provide an installation disk for engaging the outside face of the annular member, and a bolt extending through the disk with the threaded portion engaging a threaded bore in the end of the shaft. When the bolt is tightened to a specified torque, the pitman arm is properly installed.
Prior to the present invention, the art teaches the disk is simply removed from the output shaft once the arm had been properly tightened and the involute spline connection securely made. The disk previously used is relatively thick and extends well outside the profile of the pitman arm and the end of the shaft during use. These previous disk-like installation tools, if left in position, obviously would provide interference with the left front tire of the vehicle when a full right turn is made.
Furthermore, the previous designs utilized separate retainer devices, such as set screws that are threaded and extend down through the annular collar member and engage a groove around the splined end of the shaft. These retainer set screws are intended merely for the purpose of holding the position of the pitman arm secure in the event that the pitman arm is subjected to a large outside force, such as in a collision. The retainer screws hold, even though the splines on the annular mounting collar and the end of the shaft are mutilated or substantially destroyed by an overload.
Although the prior device set forth in the Sheppard '603 patent works well and exceeds specifications of steering gear manufacturers for strength and reliability, it would be desirable to have available a combined installation and retainer device for this application, as well as other applications where a collar and shaft end are to be connected for transmitting and converting substantial rotative torques into an oscillating movement, or vice-versa. It would also be desirable to have a device of this type where the proper installation is assured in each instance.